Description
2.5 Functional description
SITRANS SL
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Operating Instructions, 12/2010, A5E01132948-04
2.5.2
Influences on the measurement
Dust load
As long as the laser beam is able to generate a suitable detector signal, the dust load in the
process gas does not influence the analytical result. By applying a dynamic background
correction, measurements can be carried out without any negative impact.
The influence of a high dust load is extremely complex, and depends on the optical path
length and particle size. The optical damping increases exponentially at longer path lengths.
Smaller particles also have a very large influence on the optical damping. With high dust
load, long path length and small particle size, the technical support at Siemens AG should be
consulted.
Temperature
The temperature influence on the absorption line is compensated by the software. A
temperature signal should be fed into the analyzer from an external temperature sensor. The
signal is then used for mathematical correction of the influence of the temperature on the
observed line strength. If the process gas temperature remains constant, a static correction
can be carried out as an alternative. Without temperature compensation, the relative error
caused by changes in the gas temperature has an extensive effect on the measurement.
An external temperature signal is recommended in most cases.
Pressure
The process gas pressure can affect the line shape of the molecular absorption line. For
known pressure values, the SITRANS SL uses a special algorithm to adapt the line shape.
Additionally, an external pressure signal can be fed to the analyzer to provide complete
mathematical compensation for the pressure influence including the density effect
(depending on application and gas).
An external pressure signal is recommended in most cases.
Interferences
The SITRANS SL is able to measure the desired gas components very selectively. In special
cases, the composition of the process gas might have an influence on the shape of the
absorption lines. This influence is compensated by analyzing the full shape of the detected
signal curve applying specific algorithms.